Receive diversity in GNSS receivers

ABSTRACT

The subject matter disclosed herein relates to receiving one or more SPS signals at two or more physically separated antennae. In an aspect, signals from the physically separated antennae may be downconverted into complex digital signals that may undergo further processing to improve one or more performance metrics related to position estimation operations, for example.

CLAIM OF PRIORITY UNDER 35 U.S.C. §120

The present application for patent is a continuation of patentapplication Ser. No. 12/491,093, entitled RECEIVE DIVERSITY IN GNSSRECEIVERS, filed Jun. 24, 2009, pending, and assigned to the assigneehereof and hereby expressly incorporated by reference herein.

BACKGROUND

1. Field:

The subject matter disclosed herein relates to receiving a wirelesssignal transmitted from a communication system such as, for example, aglobal navigation satellite system.

2. Information:

A satellite positioning system (SPS) may comprise a system oftransmitters positioned to enable entities to determine their locationon the Earth based, at least in part, on signals received from thetransmitters. Such a transmitter typically transmits a signal markedwith a repeating pseudo-random noise (PN) code of a set number of chipsand may be located on ground based control stations, user equipmentand/or space vehicles. In a particular example, such transmitters may belocated on Earth orbiting satellites. For example, a satellite in aconstellation of a Global Navigation Satellite System (GNSS) such asGlobal Positioning System (GPS), Galileo, Glonass or Compass maytransmit a signal marked with a PN code that is distinguishable from PNcodes transmitted by other satellites in the constellation. To estimatea location at a receiver, a navigation system may determine pseudorangemeasurements to satellites “in view” of the receiver using well knowntechniques based, at least in part, on detections of PN codes in signalsreceived from the satellites

FIG. 1 illustrates an application of an SPS system, whereby a mobilestation (MS) 100 in a wireless communications system receivestransmissions from space vehicles (SV) 102 a, 102 b, 102 c, 102 d in theline of sight to MS 100, and derives time measurements from four or moreof the transmissions. MS 100 may provide such measurements to locationserver 104, which determines or estimates the position of the stationfrom the measurements. Alternatively, the subscriber station 100 maydetermine or estimate its own position from this information.

Wireless communications system receivers or position location systemreceivers, such as, for example, mobile station 100 described above, mayexperience difficulties in signal acquisition and/or tracking undervarious conditions. Such conditions may include weak and/or fadingsignals, frequency drift, and noise, to name but a few examples. Theseconditions may result in, for example, reduced acquisition sensitivity,degraded data demodulation performance, reduced availability of signals,diminished measurement quality, and increases in “time to fix” (TTF) fora position determination.

SUMMARY

In one aspect, one or more wireless signals may be received at two ormore physically separated antennae of a mobile station. The two or moreantennae may provide a respective two or more radio frequency signals toa receiver of the mobile station. One or more of said radio frequencysignals may be downconverted in one or more respective paths of thereceiver to generate one or more intermediate frequency signals, and theone or more intermediate frequency signals may be converted to one ormore complex digital signals comprising in-phase and quadraturecomponents. The one or more complex digital signals may be processed toperform position estimation operations, including detecting one or morepeaks.

BRIEF DESCRIPTION OF THE FIGURES

Non-limiting and non-exhaustive examples will be described withreference to the following figures, wherein like reference numeralsrefer to like parts throughout the various figures.

FIG. 1 is a block diagram of an example satellite position system (SPS)including a mobile station.

FIG. 2 is a schematic block diagram of an example mobile stationreceiver.

FIG. 3 is a schematic block diagram of an example non-coherent combinerunit.

FIG. 4 is a schematic block diagram of an example coherent combinerunit.

FIG. 5 is a schematic block diagram of an example offline coherentcombiner unit.

FIG. 6 is a schematic block diagram of an example phase estimation unit.

FIG. 7 is a schematic block diagram of an example selection diversityconfiguration.

FIG. 8 is a schematic block diagram of an example scanning diversityconfiguration.

FIG. 9 is a schematic block diagram of an example mobile receiver andnon-coherent signal combiner for a mobile station.

FIG. 10 is a schematic block diagram of an example mobile receiver andcoherent signal combiner for a mobile station.

FIG. 11 is a flow diagram of an example embodiment of a method forprocessing one or more wireless signals at a receiver with two or morephysically separated antennae.

FIG. 12 is a schematic diagram of a system for processing signals todetermine a position location according to one aspect.

FIG. 13 is a schematic diagram of a mobile station according to oneaspect.

DETAILED DESCRIPTION

As discussed above, wireless communications system receivers or positionlocation system receivers, such as, for example, mobile station 100described above, may experience difficulties in signal acquisitionand/or tracking under various conditions, such as, for example, weakand/or fading signals, frequency drift, and noise. These conditions mayresult in reduced acquisition sensitivity, degraded data demodulationperformance, reduced availability of signals, diminished measurementquality, and increases in “time to fix” (TTF) for a position estimation,for example.

In one aspect, to improve mobile station receiver performance in lightof the above-mentioned conditions, a receiver may incorporate two ormore physically separated antennae. A signal transmitted by an SPS maybe received at the two or more physically separated antennae, and thesignals received at the separate antennae may undergo different wirelesschannel conditions. Combining the signals from the different paths maysignificantly improve signal quality in such circumstances. Further,combining signals from different paths may aid in removing at least somethermal noise, in at least some circumstances.

In another aspect, samples from the two or more spatially separatedantennae may be combined using various combining algorithms, including,for example, non-coherent and coherent algorithms. Selection and/orscanning algorithms may also be employed, as discussed more fully below.The combining of the signals may result in various advantages including,for example, improved acquisition and tracking sensitivity for GNSSsignals, improved data demodulation performance, increased availabilityof signals, enhanced measurement quality, and/or decreases in TTF forposition estimation operations.

Under conditions where a signal is fading, the result may be a decreasein received signal strength. However, if the fading signal is receivedat two physically separated antennae, it is less likely that signals atboth antennae will be subject to similar fading. That is, the signalsreceived at the different antennae may fade in a less correlatedfashion. Example combining techniques described herein may make use ofthis property to improve receiver sensitivity. Improvements may also begained in noisy environments where combining the signals received at thephysically separated antennae may result in up to 1.5-3dB improvement,for example. The use of two or more physically separate antennae may bereferred to as “spatial diversity.”

As used herein, the term “mobile station” (MS) refers to a device thatmay from time to time have a position location that changes. The changesin position location may comprise changes to direction, distance,orientation, etc., as a few examples. In particular examples, a mobilestation may comprise a cellular telephone, wireless communicationdevice, user equipment, laptop computer, other personal communicationsystem (PCS) device, personal digital assistant (PDA), personal audiodevice (PAD), portable navigational device, and/or other portablecommunication devices. A mobile station may also comprise a processorand/or computing platform adapted to perform functions controlled bymachine-readable instructions. In the following discussion, variousadditional example aspects of a mobile station are described.

FIG. 2 is a schematic block diagram of an example mobile stationreceiver front end circuit 200. In an aspect, mobile station 100 maycomprise receiver front end circuit 200. For the present example,antenna 210 and antenna 220 are included. Antenna 210 in an aspect maybe associated with a receiver path including a Band Pass Filter (BPF)211, a low noise amplifier (LNA) 212, and a complex downconverter 213.The receiver path for this example also includes a baseband filter 251and an analog-to-digital converter 261. Antenna 220 in another aspectmay be associated with an additional, separate receiver path including aBPF 221, an LNA 222, and a complex downconverter 223. The separatereceiver path may also include a baseband filter 252 and ananalog-to-digital converter 262. In one aspect, antennae 210 and 220 maycomprise any antenna capable of receiving radio frequency signals. Inanother aspect, antennae 210 and 220 may be physically separated by somedistance. For one example, the distance may comprise approximately thewavelength of the signal expected to be received at the antennae. Ofcourse, this is merely one example distance by which the antennae may beseparated, and the scope of claimed subject matter is not limited inthis respect.

In an aspect, complex downconverters 213 and 223 may be provided with anoscillating signal from local oscillator (LO) 430. In this manner, asingle oscillator may be used for both complex downconverters. However,the scope of claimed subject matter is not limited in this respect. Inanother aspect, complex downconverter 213 may receive a higher frequencyreal signal from LNA 212 and may utilize the signal provided by LO 230to downconvert the signal from LNA 212 to a lower frequency complexsignal that may be provided to baseband filter 251. The lower frequencycomplex signal generated by complex downconverter 213 may be referred toas an analog baseband signal comprising in-phase and quadraturecomponents. Similarly, complex downconverter 223 may utilize the signalprovided by LO 230 to downconvert the higher frequency real signalreceived from LNA 222 to a complex analog baseband signal that may beprovided to baseband filter 252.

As used herein, “downconversion” is related to transforming an inputsignal having a first frequency characteristic to an output signalhaving second frequency characteristic. In one particularimplementation, although claimed subject matter is not limited in thisrespect, such a downconversion may comprise transformation of a firstsignal to a second signal, where the second signal has a frequencycharacteristic of a lower frequency than that of the first signal. Here,in particular examples, such a downconversion may comprisetransformation of a radio frequency (RF) signal to a baseband signaland/or baseband information. However, these are merely examples of adownconversion and claimed subject matter is not limited in thisrespect.

Analog-to-digital converter (ADC) 261 may receive the analog basebandsignal from baseband filter 251 and may generate a complex digitalsignal S1 201 comprising in-phase and quadrature components. ADC 262 mayreceive the analog baseband signal from baseband filter 252 and maygenerate a second, separate complex digital signal S2 202. A digitalbaseband processing engine may then process complex digital signals S1201 and S2 202 to perform navigation operations, to name merely oneexample application. As will be described below, complex digital signalsS1 201 and S2 202, derived from signals received at the physicallyseparate antennae, may be combined or otherwise utilized using any ofthe various example combining, scanning, and/or selecting algorithmsdescribed below to improve any of a number of performance aspects of themobile station.

Although examples described herein disclose two antennae and tworeceiver front end paths, other examples may utilize more than twoantennae and receiver front end paths. Also, although the two receiverfront end signal paths depicted in receiver front end 200 of FIG. 2 aredescribed as retaining separate paths from the antennae to the output ofADCs 261 and 262, other examples in accordance with claimed subjectmatter may combine the signal paths at some point in order to sharecomponents, for example. Combined signals may be separated at anotherpoint by a complex downconversion process, thereby restoring separatebaseband signals and signal paths. However, this is merely an example ofhow some functions of a receiver front end may be combined, and thescope of claimed subject matter is not limited in this respect. Further,although examples described herein are centered around GNSS receivers,the scope of claimed subject matter is not limited in this respect, andthe various aspects disclosed herein may be generalized for use innon-GNSS receivers.

FIG. 3 is a schematic block diagram of an example non-coherent combinerunit 310. As discussed above, to improve mobile station receiverperformance in light of various signal degrading conditions, a mobilestation may incorporate two or more physically separated antennae. Asignal transmitted by an SPS may be received at the two or morephysically separated antennae, and the signals received at the separateantennae may undergo different wireless channel conditions. Combiningthe signals from the different paths may significantly improve signalquality and improve mobile station performance in signal acquisition andtracking.

For the example of FIG. 3, example receiver front end 200, describedabove and depicted in FIG. 2, may generate two complex digital signalsS1 201 and S2 202. The two complex digital signals for this example maybe non-coherently combined to produce a combined digital signal 315 thatmay be used for position estimation operations, to name but one exampleapplication. Combined digital signal 315 in one aspect may undergocorrelation peak detection operations in preparation for additionalprocessing by a measurement and location engine as part of positionestimation operations for the mobile station.

Non-coherent combiner 310 may comprise a first unit 311 where the twocomplex digital signals S1 and S2 may undergo despreading and rotationoperations using techniques known to those of ordinary skill in the art,for example. Also, coherent accumulation and non-coherent accumulationoperations may be performed. The resulting sample streams S1′ 301 andS2′ 302 may be received at a combiner unit 312, which for the presentexample may comprise a non-coherent accumulation combiner. Combiner 312may generate combined digital signal 315.

It should be observed that for the non-coherent combining example ofFIG. 3, two separate branches are maintained until signals are combinedat non-coherent combiner 312. In an aspect, separate branches aremaintained for the rotation and despreading operations, and for thecoherent and non-coherent accumulations performed at unit 311. Theresulting sums of the non-coherent accumulations for each branch areadded within the non-coherent combiner 312, in one aspect. For thepresent example, S1′ 301 and S2′ 302 represent rotated and despread S1and S2 signals, respectively, that have further undergone coherentaccumulations followed by non-coherent accumulations. Continuing withthe present example, let

$\begin{matrix}{{{S\; 1^{\prime}} = {\sum\limits_{j = 1}^{K}\left( {\left( {\sum\limits_{i = 1}^{M}I_{i,1}} \right)^{2} + \left( {\sum\limits_{i = 1}^{M}Q_{i,1}} \right)^{2}} \right)}}{and}{{S\; 2^{\prime}} = {\sum\limits_{j = 1}^{K}\left( {\left( {\sum\limits_{i = 1}^{M}I_{i,2}} \right)^{2} + \left( {\sum\limits_{i = 1}^{M}Q_{i,2}} \right)^{2}} \right)}}} & (1)\end{matrix}$

where I_(i,1), Q_(i,1), I_(i,2), Q_(i,2) are the in-phase and quadraturesamples for the two branches for S1 and S2 and {M_(y)%} are the numberof coherent and non coherent summations respectively. The summationsinside the inner brackets in Equation 1 represent the coherentaccumulation operations of unit 311, and the summations of the elementswithin the outer brackets represent the non-coherent accumulationoperations of unit 311, for the present example. To produce combineddigital signal 315, non-coherent combiner 312 produces k₁S1′+k₂S2′ atits output where k₁,k₂ represent combining weight values. Of course,weighting techniques are not limited to the {0,1} scheme describedabove. Rather, this is merely one example weighting technique, and thescope of claimed subject matter is not limited in this respect.

As previously mentioned, combined signal 315 may be subject to furtherprocessing similar to what may occur in receivers with single antennasto identify correlation peaks and to provide measurements fornavigational operations, for one example application. However, becausefor this example two signals from physically separated antennae havebeen combined, signal integrity may be improved, and receiverperformance may therefore be enhanced.

In an aspect, the two paths for signal streams S1 and S2 may havedifferent group delay characteristics, resulting at least in part fromsuch factors as temperature effects, filter effects, manufacturingprocess variables, and/or distance between the two antennae, to name buta few example factors. In order to compensate for such group delays,mobile station 100 may perform self-calibration operations tosynchronize the paths of the receiver. In an aspect, theself-calibration operations may comprise measuring the difference in thedelays from each path of the receiver if observable signals are present.The measured difference may be utilized to adjust the timing of one ofthe paths in order to synchronize the paths. In another aspect, theself-calibration operation may be performed as part of the manufacturingprocess for the receiver and/or the mobile station. Alternatively, theself-calibration operation may be performed in the field. Theself-calibration operation may be performed a single time in one aspect,or may be performed either periodically and/or as needed in anotheraspect. Of course, the scope of claimed subject matter is not limited toany particular frequency and/or schedule for performing self-calibrationoperations. Further, in another aspect, self-calibration operations maybe performed for any of the examples described herein.

FIG. 4 is a schematic block diagram of an example coherent combiner unit410. As with the example of FIG. 3, described above, to improve mobilestation receiver performance in light of various signal degradingconditions, a mobile station may incorporate two or more physicallyseparated antennae coupled to receiver front end 200 with multiplepaths, and combining the signals from the different paths may improvesignal quality.

For the example of FIG. 4, example receiver front end 200, describedabove and depicted in FIG. 2, may generate two complex digital signalsS1 201 and S2 202. The two complex digital signals for this example maybe coherently combined by coherent combiner unit 410 to produce acombined digital signal 415 for use in position estimation operations,to name but one example application. Combined digital signal 415 in oneaspect may undergo peak detection operations in preparation foradditional processing as part of position estimation operations for themobile station, to name but one example application.

Coherent combiner 410 may comprise a first unit 411 where the twocomplex digital signals S1 201 and S2 202 may undergo despreading androtation operations using techniques known to those of ordinary skill inthe art, for example. Also, a coherent accumulation operation may beperformed at unit 411. The resulting sample streams S1′ 401 and S2′ 402may be received at a coherent combiner 412. Combiner 412 may generate acoherent sample stream S_(coh) 403 that may undergo a non-coherentsummation at unit 413 to produce combined digital signal 415. Theseoperations may be performed on a per satellite basis, in one aspect,although the scope of claimed subject matter is not limited in theserespects.

It should also be observed that for the coherent combining example ofFIG. 4, two separate branches are maintained until the signals arecombined at coherent combiner 412. In an aspect, separate branches aremaintained for the rotation and despreading operations, and are furthermaintained for the coherent accumulation performed at unit 411. Theresulting sums of the coherent accumulations for each branch arepresented to coherent combiner 412, and the non-coherent summation maybe performed on the combined stream at unit 413. For the presentexample, S1′ 401 and S2′ 402 represent rotated and despread S1 and S2signals, respectively, that have further undergone coherentaccumulations in unit 411. Continuing with the present example, let

$\begin{matrix}{{{S\; 1^{\prime}} = {\sum\limits_{i = 1}^{M}\left( {I_{i,1} + {j\; Q_{i,1}}} \right)}},{{S\; 2^{\prime}} = {\sum\limits_{i = 1}^{M}\left( {I_{i,2} + {j\; Q_{i,2}}} \right)}}} & (2)\end{matrix}$where I_(i,1), Q_(i,1), I_(i,2), Q_(i,2) are the in-phase and quadraturesamples for the two branches for S1 and S2 and M is the number ofcoherent summations.

Coherent combiner 412 may estimate the phase difference {circumflex over(θ)} between the two branches and rotate one of the branches to align itin phase with the other branch and sum the two signal streams from thetwo respective branches to produce a single stream of {I_(coh), Q_(coh)}samples. The coherent combined stream S_(coh) 403 is given for thisexample byS _(coh) =S1′*e ^(j{circumflex over (θ)}) +S2′=I _(coh) +jQ _(coh)  (3)

The combined {I_(coh), Q_(coh)} samples from stream 403 may benon-coherently summed according to

$\begin{matrix}{{combined\_ signal} = {\sum\limits_{i = 1}^{K}\left( {I_{coh}^{2} + Q_{coh}^{2}} \right)}} & (4)\end{matrix}$to generate combined digital signal 415. As with the previous examples,combined signal 415 may be subject to further processing similar to whatmay occur in receivers with single antennas to identify the peak and toprovide measurements for navigational operations, for one exampleapplication. However, because for this example two signals fromphysically separated antennae have been combined, signal integrity maybe improved, and receiver performance may therefore be enhanced.

FIG. 5 is a schematic block diagram of an example tracking unit 510. Forthis example, signals from the two branches may be combined duringtracking operations, which may improve tracking performance. Also forthis example, the two paths perform their own processing includingrotation and despreading operations at unit 511, and coherentaccumulations also at unit 511.

In an aspect, two phase locked loop (PLL) units 520 and 530 may receivestreams 501 and 502 of coherent samples from unit 511 following therotation, despreading, and coherent accumulation operations of unit 511.In an aspect, PLL units 520 and 530 may comprise Costas PLL units,although the scope of claimed subject matter is not limited in thisrespect. PLL units 520 and 530 may provide phase estimation and phaserotation for the two respective paths. The phase rotated sample streams521 and 531 from PLL units 520 and 530, respectively, may be coherentlyintegrated at coherent combiner 540 to generate a combined digitalsignal 545 that may be provided to a position engine, for example. Inother aspects, the improved quality and availability of the integratedsamples from combined digital signal 545 may be utilized advantageouslyin other operations such as, for example, loss of lock detection, signalstrength estimation, improved data demodulation, and improved bit errorrate (BER).

FIG. 6 is a schematic block diagram of example PLL unit 520. For thisexample, PLL unit 520 comprises a phase rotation unit 522, a phasediscriminator 524, a loop filter 526, and a scale function 528. Asmentioned previously, PLL unit 520 receives the stream of coherentsamples 501 from one of the two branches, and generates a stream ofphase rotated samples 521 to be delivered to coherent combiner 540.Scale values may also be transmitted from PLL 520 to combiner 540. Forthe present example, the inputs to phase rotation unit 522 and scalefunction 528 comprise the coherent samples {I, Q} with a pre-detectionintegration (PDI) or coherent integration period of 20 ms. Also, for thepresent example, scale function unit 528 may utilize a smoothed estimateof

scale=Σ(I²+Q²) using single pole smoothing with parameter α=0.9,corresponding for this example to a time constant of 10 PDI samples. Thefiltered scale function may be expressed as follows:scale_filtered=a*scale_filtered+(1−α)*scale  (5)

In another aspect, the loop bandwidth for the example of FIG. 6 may be1.0 Hz for the present example, and the loop iteration rate may beselected to be 50.0 Hz. However, these are merely example bandwidth andloop iteration values, and the scope of claimed subject matter is notlimited in this respect. Further, the outputs of PLL unit 520 maycomprise the rotated samples {I_(rot), Q_(rot)} as mentioned previouslyalong with the PLL state. Also, for the present example, the rotatedsamples from PLL units 520 and 530 may be coherently summed by coherentcombiner 540 according to the following:

$\begin{matrix}\frac{\left( {{{Scale}_{1}*I_{{rot},1}} + {{Scale}_{2}*I_{{rot}\; 2}}} \right)}{{Scale}_{1} + {Scale}_{2}} & (6)\end{matrix}$

In another aspect, a selection may be made between the two branches ofrotated samples generated by PLL units 520 and 530, respectively. Theselection may be made in order to utilize one branch at a time ratherthan combining the two branches. For one example, the selection may bemade every 20 ms, although the scope of claimed subject matter is notlimited in this respect. In another aspect, the selection may be based,at least in part, on a smoothed I_(rot), with the larger of the twovalues determining the selected branch.

FIG. 7 is a schematic block diagram of an example selection diversityconfiguration comprising receiver front end 200, a unit 710 forperforming rotation, despreading, coherent accumulation, andnon-coherent accumulation operations, a peak processing unit 720, and ameasurement and position engine 730. As used herein, the term “selectiondiversity” refers to a process of selecting one of two or more signalstreams, or branches. As can be seen in the example of FIG. 7, the twoexample signal streams or branches remain separate all of the way fromreceiver front end 200 to measurement and position engine 730. The twobranches are not combined in this example at any point. Peak processingmay be performed by unit 720, and measurements from both branches may beprovided to measurement and position engine 730. For the presentexample, measurement and position engine 730 may determine which of thetwo branches to use in position calculations. A confidence indicator mayalso be provided to measurement and position engine 730. In one aspect,the confidence indicator may comprise estimated signal strengths for thetwo branches.

In another aspect, the selection diversity example of FIG. 7 may beutilized with a tracking coherent combiner such as that discussed aboveand as depicted in FIG. 5. In such an implementation, measurement andposition engine 730 may receive inputs from peak processing unit 720,and may also receive inputs from the tracking combiner.

FIG. 8 is a schematic block diagram of an example scanning diversityconfiguration. As used herein, the term “scanning diversity” refers to atechnique of scanning two of more antennae, and selecting one of theantennae based at least in part on a performance metric. The selectedpath may be used for a fixed duration or until the performance metriccomputed based on one or more signals received at the selected antennadegrades below a programmable threshold, which triggers a new scan todetermine the better performing path. As depicted in FIG. 8, a pair ofantennae 810 and 820 are provided. Either of the antennae may beselected depending at least in part on a determination made by adecision unit 870. The selected antenna may provide radio frequency (RF)front end 830 with an RF signal received from a GNSS, for one example.Various example aspects related to the performance metric are discussedbelow.

In another aspect, a measurement engine 850 may receive a sample streamfrom baseband processing unit 840, and information from measurementengine 850 may be provided to position engine 860. Decision unit 870 mayreceive a decision metric from either measurement engine 850 for a“single shot” application such as an E911 call, for example, or fromposition engine 860 for continuous navigation applications, for anotherexample. As may be seen in FIG. 8, a single receiver chain comprising RFfront end 830 and baseband processing unit 840 may be shared between thetwo antennae. Thus, one advantage of this implementation is reducedcost. However, because measurements from signals from both antennae arenot available at the same time, performance improvements may not bequite as significant as with the example selection diversityimplementation discussed above.

Depending on whether the intended application is a single shot type ofapplication such as an E911 call, or whether the application is acontinuous navigation application, the operation of the example of FIG.8 may vary in some respects. For example, for an E911 call, the decisionmetric provided to decision unit 870 may be based at least in part on ameasurement from measurement engine 850, while for a continuationnavigation application the decision may be based at least in part onposition from position engine 860.

For a single shot application, the application may be constrained by aparticular quality of service (QoS). For example, an E911 call may havea maximum allowable time for obtaining a single position fix. Ingeneral, for one example implementation, a shallow search may beperformed using each of the two antennae. An antenna may be selectedbased on decision metrics obtained as a result of the shallow searches,and processing may continue using the selected path.

To explain the present example in a bit more detail, for the single shotapplication implementation the process may begin with the antenna 810. Ashallow search, also referred to as a shallow mode acquisition, may beperformed using a signal received from antenna 810, and a performancemetric may be estimated and stored based at least in part onmeasurements obtained from the signal provided by antenna 810. For oneexample implementation, the performance metric may comprise the numberof satellites acquired during the shallow search. Another exampleperformance metric may be an estimated average signal strength acrossall acquired satellites. As used herein, the term “shallow search”relates to a relatively fast search compared to a QoS time constraint.Of course, these are merely example performance metrics, and the scopeof claimed subject matter is not limited in this respect.

At least in part in response to storing the performance metric fromantenna 810, the algorithm may switch to antenna 820. Another shallowsearch is performed, this time using the signal received at antenna 820.A performance metric based on measurements from the signal from antenna820 may be estimated and stored. The stored metrics may be compared, andan appropriate antenna selected. The selection may be based, at least inpart, on the antenna with the most advantageous performance metric.Processing may continue using the selected antenna until the single shotapplication has completed. Of course, the algorithm described above ismerely an example, and the scope of claimed subject matter is notlimited to the particular techniques and operations described.

In another aspect, for a continuous tracking or navigation application,if the receiver is operating in a least squares mode for one exampleimplementation, the performance metric may be based, at least in part,on a horizontal estimated position error reported to decision unit 870by position engine 860. As with the single shot applicationimplementation, shallow searches may be performed using signals receivedat the two respective antenna, and the performance metrics may bestored. The metrics may be compared, and the antenna with the mostadvantageous performance metric may be selected. Processing may thencontinue using that antenna for a period of time. At least in part inresponse to that period of time elapsing, a new round of shallowsearches may be performed and performance metrics obtained and comparedto make a new selection based on current conditions. In this manner, theexample scanning diversity implementation depicted in FIG. 8periodically determines which antenna is receiving the better signal,and operations are performed using that antenna until a newdetermination is made.

Alternatively, in another aspect, instead of periodically scanning theantennae to select the “best” one, processing may continue with aselected antenna until a selected performance metric for that antennafalls below a specified threshold. If the performance metric falls belowthe threshold after a minimum dwell time, the antennae may be scanned asdescribed above to determine the most appropriate antenna for theapplication.

FIG. 9 is a schematic block diagram of an example mobile receiver andnon-coherent signal combiner for a mobile station, such as mobilestation 100 depicted in FIG. 1. The mobile station for this examplecomprises antennae 901 and 902 coupled to SPS baseband units 903 and904, respectively. SPS baseband unit 903 may comprise a receiver frontend path such as that depicted in FIG. 2, for one example. Similarly,SPS baseband unit 904 may comprise a separate receiver path. SPSbaseband units 903 and 904 provide complex digital signals tocorrelation engines 907 and 908, respectively.

Correlation engine 907 and frequency/phase control unit 915 may performa coherent accumulation. Similarly, for the other branch, correlationengine 908 and frequency/phase control unit 916 may perform a coherentaccumulation. Non-coherent integrations may be performed in the twobranches at units 911 and 912, respectively, and the results of theintegrations are stored in energy grids 913 and 914, respectively.

In another aspect, peak pre-processing of the two data streams may occurat unit 920, and the two streams may be combined by a non-coherentcombiner 930 to generate a combined digital signal to provide to peakprocessing unit 940. For the present example, peak pre-processing maycomprise determining whether a signal is present at the respectivebranches. Non-coherent combiner 930 for this example may comprise acombiner similar to non-coherent combiner 312, discussed above inconnection with FIG. 3. In an aspect, non-coherent combiner 930 mayutilize a weighted combining technique if it is known that antennas 901and 902 have different gains. For example, if it is known that antenna902 has four dB more conducted and/or radiate loss relative to antenna901, combiner 930 may give more weight to the data stream originatingwith antenna 901. Continuing with the present example, a trackingcontrol unit 950 may receive information from peak processing unit 940,and tracking control unit 950 may in turn provide information to ameasurement engine (not shown).

It may be noted that the example of FIG. 9 comprises similarfunctionality to the example depicted in FIG. 3. However, although aparticular configuration of functional units has been described, theconfiguration and operations described are merely examples, and thescope of claimed subject matter is not limited in these respects.

FIG. 10 is a schematic block diagram of an example mobile receiver andcoherent signal combiner for a mobile station, such as mobile station100 depicted in FIG. 1. The mobile station for this example comprisesantennae 1001 and 1002 coupled to SPS baseband units 1003 and 1004,respectively. SPS baseband units 1003 and 1004 provide complex digitalsignals to correlation engines 1007 and 1008, respectively.

Correlation engine 1007 and frequency/phase control unit 1015 mayperform a coherent accumulation. Similarly, for the other branch,correlation engine 1008 and frequency/phase control unit 1016 mayperform a coherent accumulation. Coherent integrations may be performedin the two branches at units 1011 and 1012, respectively. Filteredcorrelation units 1013 and 1014 and normalize unit 1020 aid inperforming despreading and phase estimation and rotation operations.

In another aspect of the present example, coherent combiner 1010receives the two aligned sample streams from the two separate branchesand performs a coherent integration to combine the two streams. In anaspect, coherent combiner 1010 may utilize a weighted combiningtechnique if it is known that the two antennas 1001 and 1002 havedifferent gains. For example, if it is known that antenna 1002 has fourdB more conducted and/or radiate loss relative to antenna 1001, coherentcombiner 1010 may give more weight to the data stream originating withthe antenna 1001. For one example, coherent combiner 1010 may comprise acombiner similar to coherent combiner 412 described above and depictedin FIG. 4. Also for the present example, an energy grid accumulator 1030may perform a non-coherent accumulation of the combined signal generatedby coherent combiner 1010. In another aspect, a tracking control unit1050 may receive information from peak processing unit 1040, andtracking control unit 1050 may in turn provide information to ameasurement engine (not shown).

It may be noted that the example of FIG. 10 comprises similarfunctionality to the example depicted in FIG. 5. However, although aparticular configuration of functional units has been described, theconfiguration and operations described are merely examples, and thescope of claimed subject matter is not limited in these respects.

FIG. 11 is a flow diagram of an example embodiment of a method forprocessing one or more wireless signals at a receiver with two or morephysically separated antennae. At block 1110, one or more wirelesssignals may be received at the two or more physically separatedantennae. The two or more antennae may provide a respective two or moreradio frequency signals to a receiver of a mobile station. At block1120, one or more of said radio frequency signals may be downconvertedin one or more respective paths of the receiver to generate one or morecomplex digital signals comprising in-phase and quadrature components.At block 1130, the one or more complex digital signals may be processedto improve one or more performance metrics related to positionestimation operations. Various examples may include fewer than, all of,or more than blocks 1110-1130. Furthermore, the order of blocks1110-1130 is merely an example order, and the scope of claimed subjectmatter is not limited in this respect.

FIG. 12 illustrates a system for acquiring periodically repeatingsignals from space vehicles (SV) according to one example. However, thisis merely an implementation of a system that is capable of acquiringsuch signals according to a particular example and other systems may beused without deviating from claimed subject matter. As illustrated inFIG. 12 according to a particular implementation, such a system maycomprise a computing platform including a processor 1210, memory 1220,and correlator 1230. Correlator 1230 may be adapted to producecorrelation functions from signals provided by a receiver front end (notshown) to be processed by processor 1210, either directly or throughmemory 1220. Correlator 1230 may be further adapted to perform any ofthe accumulation, integration, and/or combining functions described inconnection with the various examples herein. Correlator 1230 may beimplemented in hardware, software, or a combination of hardware andsoftware. However, these are merely examples of how a correlator may beimplemented according to particular aspects and claimed subject matteris not limited in these respects.

According to an example, memory 1220 may store machine-readableinstructions which are accessible and executable by processor 1210 toprovide at least a portion of a computing platform. In a particularexample, although claimed subject matter is not limited in theserespects, processor 1210 may direct correlator 1230 to search forposition estimation signals as illustrated above and derive measurementsfrom correlation functions generated by correlator 1230, including butnot limited to the accumulation, integration, and/or combining functionsdescribed above.

FIG. 13 depicts an example mobile station 1300 incorporating multipleantenna and further incorporating receiver circuitry as described in theexamples above. Implementations of a receiver as described herein may beincorporated in any one of several devices such as, for example, amobile station, base station and/or car navigation systems. Such amobile station may comprise any of several devices such as, for example,a mobile phone, notebook computer, personal digital assistant, personalnavigation device and/or the like. Here, FIG. 13 shows a particularimplementation of a mobile station in which radio transceiver 1370 maybe adapted to modulate an RF carrier signal with baseband information,such as voice or data, onto an RF carrier, and demodulate a modulated RFcarrier to obtain such baseband information. An antenna 1372 may beadapted to transmit a modulated RF carrier over a wirelesscommunications link and receive a modulated RF carrier over a wirelesscommunications link.

Baseband processor 1360 may be adapted to provide baseband informationfrom CPU 1320 to transceiver 1370 for transmission over a wirelesscommunications link. Here, CPU 1320 may obtain such baseband informationfrom an input device within user interface 1310. Baseband processor 1360may also be adapted to provide baseband information from transceiver1370 to CPU 1320 for transmission through an output device within userinterface 1310. User interface 1310 may comprise a plurality of devicesfor inputting or outputting user information such as voice or data. Suchdevices may include, for example, a keyboard, a display screen, amicrophone, and a speaker.

SPS receiver (SPS Rx) 1380 may be adapted to receive and demodulatetransmissions from SVs through SPS antennae 1382 and 1384, and providedemodulated information to correlator 1340. Correlator 1340 may beadapted to derive correlation functions from the information provided byreceiver 1380. For a given PN code, for example, correlator 1340 mayproduce a correlation function defined over a range of code phases toset out a code phase search window, and over a range of Dopplerfrequency hypotheses. As such, an individual correlation may beperformed in accordance with defined coherent and non-coherentintegration parameters.

In an aspect, receiver 1380 may comprise a receiver front end similar toreceiver front end 200 described above in connection with FIGS. 2-7.Such receiver front ends may comprise a GNSS receiver architecture whereit is proposed to downconvert the complex signals in a primary path to afirst intermediate frequency and the complex signals in a secondary pathto a second intermediate frequency. In this way, the complex signals inthe two paths can be combined into one complex signal, which will enablesharing the same baseband filter and analog-to-digital converter, in anaspect. The two GNSS signals can be separated in baseband processors bya complex down-conversion. Other implementations for receiver 1380 arepossible, such as those example implementations described above, and thescope of claimed subject matter is not limited in this respect.

Correlator 1340 may also be adapted to derived pilot-related correlationfunctions from information relating to pilot signals provided bytransceiver 1370. This information may be used by a subscriber stationto acquire wireless communications services. Correlator 1340 may also beadapted to perform any of the accumulation, integration, and/orcombining operations described in connection with the exampleimplementations discussed above. Similarly, baseband processor 1360 mayalso be adapted to perform any of the accumulation, integration, and/orcombining operations described herein.

Channel decoder 1350 may be adapted to decode channel symbols receivedfrom baseband processor 1360 into underlying source bits. In one examplewhere channel symbols comprise convolutionally encoded symbols, such achannel decoder may comprise a Viterbi decoder. In a second example,where channel symbols comprise serial or parallel concatenations ofconvolutional codes, channel decoder 1350 may comprise a turbo decoder.

Memory 1330 may be adapted to store machine-readable instructions whichare executable to perform one or more of processes, examples,implementations, or examples thereof which have been described orsuggested. CPU 1320 may be adapted to access and execute suchmachine-readable instructions. Through execution of thesemachine-readable instructions, CPU 1320 may direct correlator 1340 toanalyze the SPS correlation functions provided by correlator 1340,derive measurements from the peaks thereof, and determine whether anestimate of a location is sufficiently accurate. However, these aremerely examples of tasks that may be performed by a CPU in a particularaspect and claimed subject matter in not limited in these respects.

In a particular example, CPU 1320 at a mobile station may estimate alocation the mobile station based, at least in part, on signals receivedfrom SVs as illustrated above. CPU 1320 may also be adapted to determinea code search range for acquiring a second received signal based, atleast in part, on a code phase detected in a first received signals asillustrated above according to particular examples. It should beunderstood, however, that these are merely examples of systems forestimating a location based, at least in part, on pseudorangemeasurements, determining quantitative assessments of such pseudorangemeasurements and terminating a process to improve accuracy ofpseudorange measurements according to particular aspects, and thatclaimed subject matter is not limited in these respects.

Although antennae 1382 and 1384 are described herein as comprising SPSantennae, that is, antennae adapted to receive SPS signals, the scope ofclaimed subject matter is not limited in this respect, and other exampleimplementations may incorporate other types of antennae. In one aspect,one or more of the antennae may comprise an antenna adapted to receivewireless cellular network signals in addition to SPS signals.

The methodologies described herein may be implemented by various meansdepending upon applications according to particular examples. Forexample, such methodologies may be implemented in hardware, firmware,software, and/or combinations thereof. In a hardware implementation, forexample, a processing unit may be implemented within one or moreapplication specific integrated circuits (ASICs), digital signalprocessors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), field programmable gate arrays(FPGAs), processors, controllers, micro-controllers, microprocessors,electronic devices, other devices units designed to perform thefunctions described herein, and/or combinations thereof.

Some portions of the detailed description included herein are presentedin terms of algorithms or symbolic representations of operations onbinary digital signals stored within a memory of a specific apparatus orspecial purpose computing device or platform. In the context of thisparticular specification, the term specific apparatus or the likeincludes a general purpose computer once it is programmed to performparticular operations pursuant to instructions from program software.Algorithmic descriptions or symbolic representations are examples oftechniques used by those of ordinary skill in the signal processing orrelated arts to convey the substance of their work to others skilled inthe art. An algorithm is here, and generally, is considered to be aself-consistent sequence of operations or similar signal processingleading to a desired result. In this context, operations or processinginvolve physical manipulation of physical quantities. Typically,although not necessarily, such quantities may take the form ofelectrical or magnetic signals capable of being stored, transferred,combined, compared or otherwise manipulated. It has proven convenient attimes, principally for reasons of common usage, to refer to such signalsas bits, data, values, elements, symbols, characters, terms, numbers,numerals, or the like. It should be understood, however, that all ofthese or similar terms are to be associated with appropriate physicalquantities and are merely convenient labels. Unless specifically statedotherwise, as apparent from the following discussion, it is appreciatedthat throughout this specification discussions utilizing terms such as“processing,” “computing,” “calculating,” “determining” or the likerefer to actions or processes of a specific apparatus, such as a specialpurpose computer or a similar special purpose electronic computingdevice. In the context of this specification, therefore, a specialpurpose computer or a similar special purpose electronic computingdevice is capable of manipulating or transforming signals, typicallyrepresented as physical electronic or magnetic quantities withinmemories, registers, or other information storage devices, transmissiondevices, or display devices of the special purpose computer or similarspecial purpose electronic computing device.

Techniques described herein may be used with any one or more of severalSPS, including the aforementioned SPS, for example. Furthermore, suchtechniques may be used with positioning determination systems thatutilize pseudolites or a combination of satellites and pseudolites.Pseudolites may comprise ground-based transmitters that broadcast a PRNcode or other ranging code (e.g., similar to a GPS or CDMA cellularsignal) modulated on an L-band (or other frequency) carrier signal,which may be synchronized with GPS time. Such a transmitter may beassigned a unique PRN code so as to permit identification by a remotereceiver. Pseudolites may be useful in situations where SPS signals froman orbiting satellite might be unavailable, such as in tunnels, mines,buildings, urban canyons or other enclosed areas. Another implementationof pseudolites is known as radio-beacons. The term “satellite”, as usedherein, is intended to include pseudolites, equivalents of pseudolites,and possibly others. The term “SPS signals”, as used herein, is intendedto include SPS-like signals from pseudolites or equivalents ofpseudolites.

A “space vehicle” (SV) as referred to herein relates to an object thatis capable of transmitting signals to receivers on the Earth's surface.In one particular example, such an SV may comprise a geostationarysatellite. Alternatively, an SV may comprise a satellite traveling in anorbit and moving relative to a stationary position on the Earth.However, these are merely examples of SVs and claimed subject matter isnot limited in these respects.

Techniques described herein may also be used to receive and processsignals for various wireless communication networks such as a wirelesswide area network (WWAN), a wireless local area network (WLAN), awireless personal area network (WPAN), and so on. The term “network” and“system” may be used interchangeably herein. A WWAN may be a CodeDivision Multiple Access (CDMA) network, a Time Division Multiple Access(TDMA) network, a Frequency Division Multiple Access (FDMA) network, anOrthogonal Frequency Division Multiple Access (OFDMA) network, aSingle-Carrier Frequency Division Multiple Access (SC-FDMA) network, andso on. A CDMA network may implement one or more radio accesstechnologies (RATs) such as cdma2000, Wideband-CDMA (W-CDMA), to namejust a few radio technologies. Here, cdma2000 may include technologiesimplemented according to IS-95, IS-2000, and IS-856 standards. A TDMAnetwork may implement Global System for Mobile Communications (GSM),Digital Advanced Mobile Phone System (D-AMPS), or some other RAT. GSMand W-CDMA are described in documents from a consortium named “3rdGeneration Partnership Project” (3GPP). Cdma2000 is described indocuments from a consortium named “3rd Generation Partnership Project 2”(3GPP2). 3GPP and 3GPP2 documents are publicly available. A WLAN maycomprise an IEEE 802.11x network, and a WPAN may comprise a Bluetoothnetwork, an IEEE 802.15x, for example. Such location determinationtechniques described herein may also be used for any combination ofWWAN, WLAN and/or WPAN.

The terms, “and,” “and/or,” and “or” as used herein may include avariety of meanings that will depend at least in part upon the contextin which it is used. Typically, “and/or” as well as “or” if used toassociate a list, such as A, B or C, is intended to mean A, B, and C,here used in the inclusive sense, as well as A, B or C, here used in theexclusive sense. Reference throughout this specification to “oneexample” or “an example” means that a particular feature, structure, orcharacteristic described in connection with the example is included inat least one example of claimed subject matter. Thus, the appearances ofthe phrase “in one example” or “an example” in various places throughoutthis specification are not necessarily all referring to the sameexample. Furthermore, the particular features, structures, orcharacteristics may be combined in one or more examples. Examplesdescribed herein may include machines, devices, engines, or apparatusesthat operate using digital signals. Such signals may comprise electronicsignals, optical signals, electromagnetic signals, or any form of energythat provides information between locations.

While there has been illustrated and described what are presentlyconsidered to be example features, it will be understood by thoseskilled in the art that various other modifications may be made, andequivalents may be substituted, without departing from claimed subjectmatter. Additionally, many modifications may be made to adapt aparticular situation to the teachings of claimed subject matter withoutdeparting from the central concept described herein. Therefore, it isintended that claimed subject matter not be limited to the particularexamples disclosed, but that such claimed subject matter may alsoinclude all aspects falling within the scope of the appended claims, andequivalents thereof.

The invention claimed is:
 1. A method, comprising: receiving one or moresatellite positioning system (SPS) signals at two or more physicallyseparated antennae of a mobile station, said two or more antennae toprovide a respective two or more radio frequency signals to a receiverof the mobile station; downconverting one or more of said radiofrequency signals in one or more respective paths of a front end of thereceiver to generate two or more complex digital signals comprisingin-phase and quadrature components; and processing the two or morecomplex digital signals at least in part to improve one or moreperformance metrics related to position estimation operations, includingcombining the two or more complex digital signals according to anon-coherent combining algorithm to generate a combined digital signal;wherein said non-coherent combining algorithm comprises despreading androtating each of the two or more complex digital signals, respectively,and combining the despread signals in a non-coherent combining operationto produce the combined digital signal.
 2. The method of claim 1,wherein said processing additionally comprises detecting one or morepeaks of the combined digital signal.
 3. The method of claim 1, whereinsaid non-coherent combining operation of said non-coherent combiningalgorithm comprises: coherently accumulating the results of thedespreading and rotating operations for the two or more complex digitalsignals, respectively; non-coherently accumulating the results of thecoherent accumulation for the two or more complex digital signals,respectively; and adding the two or more non-coherent accumulations togenerate the combined digital signal.
 4. The method of claim 3, whereinsaid adding the two or more non-coherent accumulations comprises aweighed sum depending, at least in part, on respective gains of the twoor more antennae.
 5. The method of claim 4, further comprising:performing two or more sequential shallow searches using said two ormore radio frequency signals from the respective two or more antennaeand using a single receiver path, said shallow searches to yield two ormore performance metrics associated with the respective two or moreshallow searches; and selecting at least one weight value for saidadding based at least in part on the respective gains.
 6. The method ofclaim 5, wherein said two or more performance metrics comprise numbersof space vehicles acquired from the two or more radio frequency signals,respectively.
 7. The method of claim 5, wherein said two or moreperformance metrics are based at least in part on signal strengthestimates from the two or more radio frequency signals, respectively. 8.A mobile station, comprising: two or more physically separated antennaeto receive one or more SPS signals and to provide a respective two ormore radio frequency signals; a receiver comprising two or more paths toreceive the two or more radio frequency signals from the respective twoor more antennae, the two or more paths comprising a respective two ormore complex mixers to downconvert one or more of said radio frequencysignals to generate two or more complex digital signals, each complexdigital signal comprising in-phase and quadrature components; and adigital baseband processing engine to process the two or more complexdigital signals at least in part to improve one or more performancemetrics related to position estimation operations, including a combiningunit configured to combine the two or more complex digital signalsaccording to a non-coherent combining algorithm to generate a combineddigital signal; wherein said non-coherent combining algorithm comprisesdespreading and rotating each of the two or more complex digitalsignals, respectively, and combining the despread signals in anon-coherent combining operation to produce the combined digital signal.9. The mobile station of claim 8, said digital baseband processingengine to additionally process by detecting one or more peaks of thecombined signal.
 10. The mobile station of claim 8, said non-coherentcombining operation comprises: coherently accumulating the results ofthe dispreading and rotating operations for the two or more complexdigital signals, respectively; non-coherently accumulating the resultsof the coherent accumulation for the two or more complex digitalsignals, respectively; and adding the two or more non-coherentaccumulations to generate the combined digital signal.
 11. The mobilestation of claim 10, said combining unit to add the two or morenon-coherent accumulations at least in part by utilizing a weighed sumdepending, at least in part, on respective gains of the two or moreantennae.
 12. The mobile station of claim 11, said digital basebandprocessing engine further to perform two or more sequential shallowsearches using said two or more radio frequency signals from therespective two or more antennae and using a single receiver path, saidshallow searches to yield two or more performance metrics associatedwith the respective two or more shallow searches, said digital basebandprocessing engine further to select at least one weight value for saidadd based at least in part on the respective gains.
 13. The mobilestation of claim 12, wherein said two or more performance metricscomprise numbers of space vehicles acquired from the two or more radiofrequency signals, respectively.
 14. The mobile station of claim 12,wherein said two or more performance metrics comprise signal strengthestimates from the two or more radio frequency signals, respectively.15. An apparatus, comprising: means for receiving one or more satellitepositioning system (SPS) signals at two or more physically separatedantennae of a mobile station, said two or more antennae to provide arespective two or more radio frequency signals to a receiver of themobile station; means for downconverting one or more of said radiofrequency signals in two or more respective paths of a front end of thereceiver to generate two or more complex digital signals, each complexdigital signal comprising in-phase and quadrature components; and meansfor processing the two or more complex digital signals at least in partto improve one or more performance metrics related to positionestimation operations, including means for combining the two or morecomplex digital signals according to a non-coherent combining algorithmto generate a combined digital signal; wherein said means for combiningcomprises means for despreading and rotating each of the two or morecomplex digital signals, respectively, and means for combining thedespread signals in a non-coherent combining operation to produce thecombined digital signal.
 16. The apparatus of claim 15, wherein saidmeans for processing additionally comprises means for detecting one ormore peaks of the combined digital signal.
 17. The apparatus of claim15, wherein said means for combining the the despread signals accordingto the non-coherent combining operation comprises: means for coherentlyaccumulating the results of the despreading and rotating operations forthe two or more complex digital signals, respectively; means fornon-coherently accumulating the results of the coherent accumulation forthe two or more complex digital signals, respectively; and means foradding the two or more non-coherent accumulations to generate thecombined digital signal.
 18. The apparatus of claim 17, wherein saidmeans for adding the two or more non-coherent accumulations comprisesmeans for performing a weighed sum depending, at least in part, onrespective gains of the two or more antennae.
 19. The apparatus of claim17, further comprising: means for performing two or more sequentialshallow searches using said two or more radio frequency signals from therespective two or more antennae and using a single receiver path, saidshallow searches to yield two or more performance metrics associatedwith the respective two or more shallow searches; and means forselecting at least one weight value for said means for adding based atleast in part on a comparison of the two or more performance metrics.20. The apparatus of claim 19, wherein said two or more performancemetrics comprise numbers of space vehicles acquired from the two or moreradio frequency signals, respectively.
 21. The apparatus of claim 19,wherein said two or more performance metrics are based at least in parton signal strength estimates from the two or more radio frequencysignals, respectively.
 22. An article, comprising a non-transitorystorage medium having stored thereon instructions that, if executed by aprocessor of a mobile station, direct the processor to: process two ormore complex digital signals, each digital signal comprising in-phaseand quadrature components, to perform position estimation operationsthat combine the two or more complex digital signals according to anon-coherent combining algorithm to generate a combined digital signal,wherein said non-coherent combining algorithm comprises despreading androtating each of the two or more complex digital signals, respectively,and combining the despread signals in a non-coherent combining operationto produce the combined digital signal; wherein said two or more complexdigital signals are derived from one or more SPS signals received at twoor more physically separated antennae of the mobile station.
 23. Thearticle of claim 22, wherein the storage medium has stored thereonfurther instructions that, if executed, further direct the processor todetect one or more peaks of the combined digital signal.
 24. The articleof claim 22, wherein the storage medium has stored thereon furtherinstructions that, if executed, further direct the processor to performthe non-coherent combining operation by: coherently accumulating theresults of the dispreading and rotating operations for the two or morecomplex digital signals, respectively; non-coherently accumulating theresults of the coherent accumulation for the two or more complex digitalsignals, respectively; and adding the non-coherent accumulations togenerate the combined digital signal.
 25. The article of claim 24,wherein the storage medium has stored thereon further instructions that,if executed, further direct the processor to add the non-coherentaccumulations utilizing a weighed sum depending, at least in part, onrespective gains of the two or more antennae.
 26. The article of claim25, wherein the storage medium has stored thereon further instructionsthat, if executed, further direct the processor to: perform two or moresequential shallow searches using said two or more radio frequencysignals from the respective two or more antennae and using a singlereceiver path, said shallow searches to yield two or more performancemetrics associated with the respective two or more shallow searches; andselect at least one weight value for said add based at least in part onthe respective gains.
 27. The article of claim 26, wherein said two ormore performance metrics comprise numbers of space vehicles acquiredfrom the two or more radio frequency signals, respectively.
 28. Thearticle of claim 26, wherein said two or more performance metricscomprise signal strength estimates from the two or more radio frequencysignals, respectively.
 29. The method of claim 1, wherein despreadingand rotating comprises despreading and rotating each one of the two ormore complex digital signals in a separate receiver path than each ofthe other ones of the two or more complex digital signals.
 30. Themethod of claim 3, wherein coherently accumulating comprises coherentlyaccumulating each one of the two or more complex digital signals in aseparate receiver path than each of the other ones of the two or morecomplex digital signals.
 31. The method of claim 3, whereinnon-coherently accumulating comprises non-coherently accumulating eachone of the two or more complex digital signals in a separate receiverpath than each of the other ones of the two or more complex digitalsignals.
 32. The mobile station of claim 8, wherein despreading androtating comprises dispreading and rotating each one of the two or morecomplex digital signals in a separate receiver path than each of theother ones of the two or more complex digital signals.
 33. The mobilestation of claim 10, wherein coherently accumulating comprisescoherently accumulating each one of the two or more complex digitalsignals in a separate receiver path than each of the other ones of thetwo or more complex digital signals.
 34. The mobile station of claim 10,wherein non-coherently accumulating comprises non-coherentlyaccumulating each one of the two or more complex digital signals in aseparate receiver path than each of the other ones of the two or morecomplex digital signals.
 35. The apparatus of claim 15, whereindespreading and rotating comprises dispreading and rotating each one ofthe two or more complex digital signals in a separate receiver path thaneach of the other ones of the two or more complex digital signals. 36.The apparatus of claim 17, wherein coherently accumulating comprisescoherently accumulating each one of the two or more complex digitalsignals in a separate receiver path than each of the other ones of thetwo or more complex digital signals.
 37. The apparatus of claim 18,wherein non-coherently accumulating comprises non-coherentlyaccumulating each one of the two or more complex digital signals in aseparate receiver path than each of the other ones of the two or morecomplex digital signals.
 38. The article of claim 22, whereindespreading and rotating comprises dispreading and rotating each one ofthe two or more complex digital signals in a separate receiver path thaneach of the other ones of the two or more complex digital signals. 39.The article of claim 24, wherein coherently accumulating comprisescoherently accumulating each one of the two or more complex digitalsignals in a separate receiver path than each of the other ones of thetwo or more complex digital signals.
 40. The article of claim 24,wherein non-coherently accumulating comprises non-coherentlyaccumulating each one of the two or more complex digital signals in aseparate receiver path than each of the other ones of the two or morecomplex digital signals.